Functional Near Infrared Spectroscopy (fNIRS) Explained! | Neuroscience Methods 101

Functional near infrared spectroscopy, or fNIRS, can measure brain activation by measuring oxygen levels in the brain. Here we explain how it works.

Similar to functional magnetic resonance imaging (fMRI), fNIRS measures the blood oxygen level dependent response, or BOLD response. However, both methods go about it in a different way. fNIRS uses near-infrared light, which penetrates skin and skull to shine on cortical brain tissue. Within this tissue the light is absobed at different rates. Blood with a lot of oxygen, or oxygenated blood, absorbs mainly near infrared wavelengths above 790 nm, whereas deoxygenated blood absorbs mainly wavelenghts below 790 nm.

Using these proporties, with fNIRS the ration between oxygenated and deoxygenated blood can be calculated for a given brain region. This will inform you about which of these areas is activated.

fNIRS is spatially less precise than fMRI, but it is cheaper and allows for more movement. This can be good for research on movement, or when working with pediatric or geriatric populations.

References/resources:
Boas, D. A., Elwell, C. E., Ferrari, M., & Taga, G. (2014). Twenty years of functional near-infrared spectroscopy: introduction for the special issue. NeuroImage, 85 Pt 1, 1–5. https://doi.org/10.1016/j.neuroimage....

Ehlis, A. C., Schneider, S., Dresler, T., & Fallgatter, A. J. (2014). Application of functional near-infrared spectroscopy in psychiatry. NeuroImage, 85 Pt 1, 478–488. https://doi.org/10.1016/j.neuroimage....

Ferrari, M., & Quaresima, V. (2012). A brief review on the history of human functional near-infrared spectroscopy (fNIRS) development and fields of application. NeuroImage, 63(2), 921–935. https://doi.org/10.1016/j.neuroimage....

Hoshi Y. (2007). Functional near-infrared spectroscopy: current status and future prospects. Journal of biomedical optics, 12(6), 062106. https://doi.org/10.1117/1.2804911

Pinti, P., Tachtsidis, I., Hamilton, A., Hirsch, J., Aichelburg, C., Gilbert, S., & Burgess, P. W. (2020). The present and future use of functional near-infrared spectroscopy (fNIRS) for cognitive neuroscience. Annals of the New York Academy of Sciences, 1464(1), 5–29. https://doi.org/10.1111/nyas.13948

Narrated by: Miles Wischnewski

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